As the bandwidth for data transmission increases in conjunction with development of communication technology, user demands for a high-quality service using multi-channel speech and audio are on the increase. Provision of high-quality speech and audio services requires, above all, coding technology capable of efficiently compressing and decompressing stereo speech and audio signals.
Therefore, extensive study on codecs for coding Narrow Band (NB: 300-3,400 Hz), Wide Band (WB: 50-7,000 Hz), and Super Wide Band (SWB: 50-14,000 Hz) signals are in progress. For example, ITU-T G.729.1 is a representative extension codec, which is a WB extension codec based on G.729 (NB codec). This codec provides bitstream-level compatibility with G.729 at 8 kbit/s, and provides NB signals of better quality at 12 kbit/s. In the range of 14-32 kbit/s, the codec can code WB signals with bitrate scalability of 2 kbit/s, and the quality of output signals improves as the bitrate increases.
Recently, an extension codec capable of providing SWB signals based on G.729.1 is being developed. This extension codec can encode and decode NB, WB, and SWB signals.
In such an extension codec, sinusoidal coding may be used to improve the quality of synthesized signals. When the sinusoidal coding is used, the energy of input signals needs to be considered to increase coding efficiency. Specifically, when the number of bits available for sinusoidal coding is insufficient, it is efficient to preferentially code a band that has a larger influence on the quality of synthesized signals, i.e. a band that has a relatively large amount of energy.